Spectroscopic studies of van der Waals interactions

Abstract

A review is given for determination of van der Waals interactions in condensed media by OH vibration spectroscopy. 1. Large changes of the dipole moment derivaties P 1 induced by unpolar solvents are calculated by IR intensities, demonstrating that von der Waals interactions polarize OH groups strongly. 2. The relations: interaction energies = f (Δν), IR intensities = f(Δν), p 1 = f(Δν) or Δν = f(r 0…0 are different for v.d. Waals or H-bond effects. (Δν = ν vapour = ν solution). 3. Decreasing temperatures (decreasing intermolecular distances) in diluted solutions of unpolar or weak polar solvents increase Δν linearly in the range 100 K < T < 360 K. Δν becomes constant below T < 100 K. This is related to the T linear density ϱ relations for T < T B (boiling). This linear relation could be calculated by a model of the sum of the Lennard-Jones potentials of the first and second next neighbours and its population of the quantized intermolecular vibration levels. At low T the density becomes T-independent in the model calculation as well as in experiments. Parallel we observed at very low T a T-independence of ν 01 and ν 02 in solutions. 4. Under saturation conditions Δν 02(OH) = f(T) becomes near T critical proportional to the squared densities or could be described with a simplified model of non polar liquids. 5. The T-gradient d(Δν)/dT is proportional to the shift Δν 0 for OH in solvents. The same solvent induces at different alcohols different Δν and d(Δν)/dT demonstrating that v.d. Waals forces acts on spectra by interactions between solvent and solute and could not described simplified by solvent properties but as well as by solute properties too. 6. Changing the solvent pressure till 10 GPa we observed in v.d. Waals systems: a red shift, and Δν maximum, Δν = 0 at high p and blue shifts. This result is in agreement with an extended theory summarizing the OH and the Lennard-Jones potential. This theory allows to get intermolecular potentials in condensed media by IR spectra. 7. Rare gas matrix effects on OH at low T could be plot in a common diagram as function of the OH-matrix potentials, which could be estimated by the critical T of matrix and the oscillator. This experiment stresses the dependence of the interaction between solute and solvent. 8. The T- and p-dependence of half width is discussed.